Light-sensitive diazotype layers containing magnesium salts



United States Patent LIGHT-SENSITIVE DIAZOTYPE LAYERS CON- TAINING MAGNESIUM SALTS Cari Botkin, Chicago, Ill., and John Sulich, .lr., Endicott,

N. Y., assignors to General Aniline & Film Corporation, New York, N. Y., a corporation of Delaware N 0 Drawing. Application November 20, 1951, Serial No. 257,422

1i Claims. (Cl. 95-6) This invention relates to an improvement in the production of photographic prints by the diazotype process and more particularly to the manufacture of improved light-sensitive materials for the production of photographic images by the diazo process.

In the diazotype process, the light-sensitive material containing a light-sensitive diazo compound and an azo coupling component on a suitable support such as paper, film base, or fabric, is exposed to light through a suitable pattern, for instance, a line drawing or a photographic transparency. The diazo compound is decomposed by the action of light where it is unprotected by the outlines of the pattern and its ability to combine later with the coupling component is destroyed. After exposure, the exposed layer is developed by bringing it into contact with ammonia vapors, thereby causing the coupling of the undestroyed diazo compound and the coupling component. A reproduction of the original pattern is obtained as an azo dye image on a light background. This procedure is known as the dry developing process and the sensitive material employed in the process is known as dry print material.

The sensitive dry print material is prepared with a solution containing both the diazo compound and one or more coupling components on a suitable base such as paper, textile, felt or similar absorbent, fibrous supports. For the reason that the .dyestuff components, as coated on the carrier are relatively unstable, and in order to prevent coupling prior to alkaline development, the coating solutions contain usually also small amounts of .an acid such as citric acid, tartaric acid, tricarballylic acid, phosphoric acid and the like, and a stabilizing or anti-oxidizing agent such as thiourea, allyl isothiocyanate and the like. which tion on the finished. print. Another important ingredient of diazomaterials is zinc chloride. This salt acts not only as a hygroscopic agent but also improves the keeping qualities .of the coated paper under adverse storage conditions especially those vof high humidity or dry heat. Unfortunately, the presence of zinc chloride causes an undesirable lack of brightness of the developed azo dye image and a discoloration of the background which no longer shows the inherent whiteness of the carrier, e. g., paper, but appears grayish or yellowish. Together, these two effects give the impression of an unsatisfactory visual contrast. Moreover, the developed dry print papers containing zinc chloride are neither Wash fast nor Water spot proof but bleed when brought into contact with water. Furthermore, this bleeding becomes very apparent when the papers are handled with moist fingers .and give rise to the formation of undesirable fingerprints.

We have found that the foregoing shortcomings can be obviated by replacing zinc chloride. in the light-sensitive diazo material, with a combination of zinc chloride with a water-soluble inorganic magnesium salt, the latter amounting to from to 40% by weight of the combined amounts of zinc chloride and magnesium salts. Magnesium chloride and magnesium sulfate are most suitable for this purpose. By this simple expedient, the developed azo dye images become brighter, the background whiter, and the picture as a whole shows an appreciably improved visual contrast. Moreover, the tendency ofthe paper to bleed or to show finger prints upon handling is remarkably decreased.

Amounts of zinc chloride ordinarily employed heretofore in the preparation of dry print paper range from prevent background discolorar stabilized salts, as

30 to grams per liter of a diazotypecoating solution; although amounts ranging from 40 to 80 grams are commonly preferred. Accordingly, the, amounts of magnesium salts added to the coating composition may range from 3 to 40 grams per liter, depending on the amount of zinc chloride employed. Percentages higher than 40% based on the combined Weight of zinc chloride and magnesium salts are not desirable since they affect adversely several properties of the diazo paper. Shelf life, resistance to high humidity or dry heat before development, completeness of ammonia development and Wash fastness are seriously impaired, and fading of the exposed and developed print is rapidly ac.- celerated. Reducing the amount of zinc chloride without replacing it with, the above magesium salts fails to give the desired improvement. Although these ratios are not critical, the combined amount of zinc chloride and magnesium salt is at least equal to and does not exceed by more than a factor of fifteen the amount of the stabilized, light-sensitive diazo compound employed.

In the coating solutions which are used for sensitizing the diazo paper according to this invention any combination of diazo and coupling components which are suitable for the preparation of dry development (two component diazotype layers) and which will produce the shade desired for the final image, may be employed. Diazo compounds which are suitable for such tWo component diazotype layers are known to be those which are derived from 1,2- and 2,1-aminonaphthols, 1,4-aminonaphthols and aromatic p-diamines of the benzene series, particularly p-phenylene diamines which are monoor di-substituted on one of the two amino groups. Examples of such diazo compounds which are commonly used in the production of diazotype images are the diazo derivatives of: 4-amino-N-methylaniline 4-amino-N-ethylaniline 4-aminodiphenylamine 4-amino-N (,3-hydroxyethy1) aniline 4-amino-N- 2',6'-dibromobenzyl) aniline 4-amino-N,N-dimethylaniline 4-amino-N,N-diethylaniline 4-amino-N,N-dipropylaniline =4-amino-N-methyl-N- (,fi-hydroxyethyl aniline 4-amino-N- ,B-hydroxyethyl aniline gl-amino-N-butyl-N-(,B-hydroxyethyDaniline '4-amino-N,N-di(B-hydroxyethyl) aniline 4-amino-N-benzyl-N-ethylaniline 4-amino-N-ethyl-3-methylaniline 4-amino-N,N-dimethyl-3-methylaniline -4-amino-N,N-di methyl-2-methylaniline 4-amino-N,N-diethyl-3-methylaniline 4-amn1o-N-ethy1-N- (,B-hydroxyethyl) 3-methylaniline ,4-am no-N-cyclohexyl-Z-methoxyaniline 4-am1no-N,N-di (ti-hydroxyethyl) 3-methoxyaniline 4-amino-N,N-diethylamino-3-ethoxyaniline 4-amino- N-benzyl-2,S-diethoxyaniline 4-amino-3 -chloro-N,N-di (fl-hydroxyethyl) aniline 4-amino-3-carboxy-N,N-diethylaniline l-amino-2-hydroxynaphthalene-4-sulfonic acid Z-amino-l-hydroxynaphthalene-5-sulfonic acid 2-amino-1-hydroxynaphthalene-3,6-disu1fonic acid S-aminocarbazol, and the like.

Thesediazo compounds are .used in the form of their exemplified by p-diphenylamine diazonium sulfate or in the form of their zinc chloride or boron trifluoride double salts. As examples of such stabilized double salts, there may be mentioned the zinc chloride or boron trifluoride double salts of: p-Diethylaminobenzenediazonium chloride p Di(,6-hydroxyethyl)amino 2 methylbenzenediazonium chloride p-E%1Yl (ti-hydroxyethyl)aminobenzenediazonium chlon e p-Diethylamino-3-ethoxybenzenediazonium chloride, and

the like.

Inthe case of the zinc chloride double salts, the zinc chlorlde combined therein-is excluded in calculating the .percentage or proportion of the chloride andmagw hydride l-amino 2 hydroxynaphthalene-4-sulfodiazonium anhydride l-amino 2 hydroxynaphthalene-S-sulfodiazonium anhydride and their water soluble alkali metal salts.

As examples of suitable azo coupling components, there may be mentioned:

Resorcinol Phloroglucinol 3-hydroxyphenylurea 3-(N-3 '-aminobenzoyl) aminophenol 3- (N-4-aminobenzoyl) aminophenol 2,3-dihydroxynaphthalene 2,7-dihydroxynaphthalene 2,3-dihydroxynaphthalene-6-sulfonic acid 1-hydroxynaphthalene-4-sulfonic acid 2-hydroxynaphthalene-3,6-disulfonic acid l-hydroxynaphthalene-3,8-disulfonic acid 2-amino-8-hydroxynaphthalene-3,6-disulfonic acid 2,3-dihydroxynaphthalene-6-carboxylic acid l-amino-7-hydroxynaphthalene l-amino-S-hydroxynaphthalene-3,6-disulfonic acid 4-hydroxybenzimidazole hydrochloride 2-hydroxy-7,8-naphthimidazole hydrochloride 8-hydroxy-1,2-naphthimidazole hydrochloride 7-hydroxy-1,2-naphthimidazole hydrochloride 2-hydroxynaphthalene-S-biguanide 7-hydroxynaphthalene-2-biguanide 7-hydroxynaphthalene-l-biguanide S-hydroxyuaphthalene-1-biguanide 2,2',4,4-tetrahydroxydiphenyl 3 3 ,5 ,5 -tetrahydroxybiphenyl 4-hydroxyquinolone 1-methyl-4-hydroxyquinolone (2) l-( 2-methoxyphenyl -4-hydroxyquinolone 2) 1-phenyl-3-methylpyrazolone 1- 4-sulfophenyl -3 -methylpyrazolone 1-tolyl-3-methylpyrazolone Acetoacetanilide Acetoacet-o-toluidide Acetoacetic acid benzylamide, and the like.

Sulfonic or carboxylic acid substituted couplers may be used as such or in the form of their water soluble alkali metal salts. Variations in shade may be obtained by using more than one coupler. Similarly, blacks, which are uniformly neutral throughout the full density, and half-tone ranges can be prepared by the combined use of at least three selected coupling components in accordance with the procedure described in U. S. Patent 2,537,919.

Suitable carriers for diazo solutions include not only various types of paper such as ordinary wood pulp paper, rag type paper or document paper, and photographic film base such as cellulose acetate, cellulose acetate butyrate and the like, but also textiles including fabrics made from cotton, cellulose acetate, batiste, regenerated cellulose of the xanthate or viscose type, balloon cloth, knitted rayon jersey, mixed cotton and rayon, or other absorbent, fibrous woven or felted materials which can be impregnated with the diazo solutions.

The following specific examples are intended to be illustrative and are not to be considered as limiting the invention.

Example I A wood pulp paper stock of medium weight was coated with a solution having the following composition:

Water to make 100 mls.

The resulting sensitized paper was cut into sheets and exposed to ultra-violet light under a density step wedge anddeveloped with ammonia vapors in a commerical model of an ammonia developing machine.

Another paper coated with a coating solution identical with the one described above with the exception that it did not contain any magnesium chloride and the zinc chloride concentration had been increased to 6 grams was exposed under the same wedge and developed in the same machine. The pictures on both papers were of blue color but the one on the paper containing zinc chloride and magnesium chloride displayed a brighter color, gave a better visual contrast, had a whiter background and superior wash-fastness than the picture obtained on the paper which contained zinc chloride only. These visual observations of greater brightness and contrast were confirmed by spectrophotometric measurements to which both samples were submitted.

The following results were obtained:

It will be noted that the hues and the values (lightness) of the two samples are practically identical but that the Munsell chroma of the one containing magnesium chloride and zince chloride is appreciably higher and consequently farther away from gray than the chroma of the other which contains only zinc chloride. Using the psychophysical terms of the I. C. 1. System as described in Hardys Handbook of Colorimetry, it can be stated that the magnesium chloride containing sample had a higher excitation purity for a given apparent luminous reflectance. These measurements confirmed the visual observation that the sample containing the magnesium chloride-zinc chloride mixture was brighter and showed greater visual contrast than the standard material which contained only the zinc chloride.

Example 11 A diazotype paper stock made of rag paper was coated with an aqueous solution having the following composition:

l-methyl-l-oxyquinolone-(2) gms 13.0 Zinc chloride double salt of p-diethylaminobenzenediazonium chloride gms 22.0 Ethyl alcohol mls 50.0 Citric acid gms 80.0 Thiourea gms 40.0 Zinc chlorid grm 39.0 Magnesium chloride (anhydrous) gms 13.0

Water to make 1 liter.

Example III An aqueous solution of the following composition was prepared and applied to a starch-sized cotton cloth:

Gms.

Zinc chloride double salt of p-diethylamino-Z- methylbenzenediazonium chloride 5.0 2,3-dihydroxynaphthalene 8.0 Citric acid 50.0 Zinc chloride 45.0 Magnesium chloride (anhydrous) 15.0 Saponin 0.1

Water to make 1 liter.

After drying, the cloth was exposed to ultra-violet light under a photographic transparency and developed by means ofmoist, warm ammonia vapors. The .color obtamedwas a bright hluehavingrexcellent gradation char-- acteristics and was superior in both respects IO-,3 picture obtained on a comparison coating,whichhad-be'en prepared .in an identical manner with the exception that the 45 grams of zincchloride had been replaced by 60 grams of zinc chloride and the magnesium chloride had beenomitted entirely. Moreover, the magnesium .chloridercontaining print showed better fastness-to washing thamthetypesample with contained only zinc chloride.

Example IV An aqueous solution of the following-composition was prepared and applied to a linen paper:

Isopropanol mm 10.0 Ethylene glycol mls 50;0 Citric acid ems 50.0 Thiourea g ns 5.0.0 Saponin gms 01 Zinc chloride double salt of p-diethylaminobenzene diazonium chloride gms 20.0 2-hydroxy-7,8-naphthimidazole hydrochloride gms 20.0 Zinc chlor gms 35.0 Magnesium-chloride (anhydrous)- gms 15.0

Water tomake 1 liter.

The" resulting diazo paper was 'exposed to ultra-violet light under a pattern and subsequently developed with warm, moist ammonia vapors. A maroon print was obtained which showed better background whiteness and more brilliant colors than comparison prints which had been prepared from two coating solutions which were identical to those above except that they contained no magnesium chloride and the zinc chloride concentration had been changed to 35 and 50 grams respectively. Moreover, the magnesium chloride containing print displayed a far better wash-fastness than the comparison prints which contained zinc chloride only.

Example V A solution having the following composition was prepared and coated on a diazotype paper stock made of rag paper:

Resorcinol gms 25.0 Zinc chloride double salt of N-methyl-N-(fi-hydroxyethyl)aminobenzenediazonium chloride gms 50.0 Citric a gms 60.0 Thiourea gms 45.0 Isopropanol mls 15.0 Saponin g ns 0.1 Zinc chloride gms 40.0 Magnesium chloride (anhydrous) ..gms 15.0 Water to make 1 liter. After drying, the paper was exposed to ultra-violet light under a translucent sheet having printed matter thereon and developed in an atmosphere of ammonia. A brilliant sepia picture was formed which showed a greater visual contrast, a whiter background and greater brilliance than comparison pictures obtained on papers prepared from coating solutions identical with the one above except that the magnesium chloride had been omitted and the amount of zinc chloride had been increased from 40 grams to 45 and 55 grams respectively.

Example VI A coating solution having the following comopsition Water to make 1 liter.

The paper was allowed to dry and then exposed to ultraviolet light under a transparency. The exposed samples were developed in a warm and humid atmosphere containing ammonia vapors. A black reproduction of the-transparency wasobtained which was characterized,

by a whiter background, greater visual contrast, greater luster, and better wash-fastness than comparison prints which .hadbeen coated with the coating solution which was identical with the one above with the exception that magnesium chloride had been omitted and the zinc,

chlorideconcentration had been increased from 30 grams to 50 grams.

7 Example VII A regenerated cellulose cloth of the viscose type was.

impregnated with an. aqueous solution having .the fol lowing composition:

Wated to make 1 liter.

After drying, the cloth was exposed to ultra-violet light undersa photographic transparency and developed with moist, Warm ammonia vapors. abright blue having excellent gradation characteristics. Its brightness and gradation were superior to those of a picture obtained on a control coating which had been prepared in an identical manner, with exception that the 40 grams of zinc chloride had been replaced by 65 grams of zinc chloride and the magnesium sulfate had been omitted entirely. Furthermore, the magnesium sulfate-containing print showed substantially better fastness to washing than the control sample which contained only zinc chloride.

While there are disclosed above a number of embodiments of the invention herein described, it is obvious that various changes may be made without departing from the nature and spirit of the invention. Therefore, the invention is not limited to the specific details herein described except as defined in the appended claims.

We claim:

1. A diazotype light-sensitive material comprising on a suitable base a stabilized light-sensitive diazo compound and a coupling component, together with zinc chloride and a water-soluble, inorganic magnesium salt, the quantity of the magnesium salt being more than ten per cent (10%) and less than forty per cent (40%) by weight of the total quantity of zinc chloride and magnesium salt combined.

2. A light-sensitive printing material for use in the production of diazotype prints comprising an absorbent fibrous support impregnated with a stabilized light-sensitive diazo compound and an azo coupling component together with zinc chloride and a water-soluble inorganic magnesium salt, the quantity of the magnesium salt being more than ten per cent 10%) and less than forty per cent (40%) by weight of the total quantity of zinc chloride and magnesium salt combined.

3. A light-sensitive diazotype photoprinting material comprising a paper support coated with a sensitizing solution containing a stabilized light-sensitive diazo compound and an azo coupling component, together with zinc chloride and magnesium chloride, the quantity of the magnesium chloride being more than ten per cent 10%) and less than forty per cent (40%) by Weight of the total quantity of zinc chloride and magnesium chloride combined.

4. light-sensitive diazotype photo-printing material comprising a paper support coated with a sensitizing solution containing a stabilized li ht-sensitive diazo compound and an azo coupling component together with zinc chloride and magnesium sulfate, the quantity of the magnesium sulfate being more than ten per cent (10%) and less than forty per cent (40%) by weight of the total quantity of zinc chloride and magnesium sulfate combined.

5. The process of producing a diazotype photoprinting material which comprises applying a solution comprising a stabilized light-sensitive diazo compound, at least one coupling component, zinc chloride and a water-soluble, inorganic magnesium salt, the quantity of the magnesium salt being more than ten per cent (10%) and less than forty per cent (40%) of the total quantity of zinc mls 200.0.

The color obtained ,was.

7 chloride and magnesium salt combined, to a suitable carrier and drying.

6. The process of producing a photoprinting material which comprises impregnating an absorbent, fibrous support with a solution comprising a stabilized light-sensitive diazo compound and at least one coupling component together with zinc chloride and a water-soluble, inorganic magnesium salt, the quantity of the magnesium salt being more than ten per cent (10%) and less than forty per cent (40%) of the total quantity of zinc chloride and magnesium salt combined, and drying.

7. The process of producing a photoprinting material which comprises coating a paper base with a solution comprising a stabilized light-sensitive diazo compound and a coupling component together with zinc chloride and magnesium chloride, the quantity of the magnesium chloride being more than ten per cent 10%) and less than forty per cent (40%) of the total quantity of zinc chloride and magnesium chloride combined, and drying.

8. The process of producing a photoprinting material which comprises coating a paper base with a solution comprising a stabilized light-sensitive diazo compound and a coupling component together with zinc chloride and magnesium sulfate, the quantity of the magnesium sulfate being more than ten per cent (10%) and less than forty per cent (40%) of the total quantity of zinc chloride and magnesium sulfate combined, and drying.

9. A diazotype light-sensitive material according to claim 1 wherein the combined quantity of zinc chloride and magnesium salt is at least equal to and does not exceed, by more than a factor of fifteen, the quantity of the stabilized light-sensitive diazo compound employed.

10. The process of producing a diazotype photoprinting material according to claim 1 wherein the combined quantity of zinc chloride and magnesium salt is at least equal to and does not exceed, by more than a factor of fifteen, the quantity of the stabilized light-sensitive diazo compound employed.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,973,148 Kemmerich Sept. 11, 1934 2,537,097 Slifkin Jan. 9, 1951 2,541,178 Slifkin Feb. 13, 1951 2,552,354 Von Glahn May 8, 1951 FOREIGN PATENTS Number Country Date 284,253 Great Britain Dec. 16, 1927 443,955 Great Britain Mar. 10, 1936 571,802 Great Britain Sept. 10, 1945 

1. A DIAZOTYPE LIGHT-SENSITIVE MATERIAL COMPRISING ON A SUITABLE BASE A STABLIZIED LIGHT-SENSITIVE DIAZO COMPOUND AND A COUPLING COMPONENT, TOGETHER WITH ZINC CHLORIDE AND A WATER-SOLUBLE, INORGANIC MAGNESIUM SALT, THE QUANTITY OF THE MAGNESIUM SALT BEING MORE THAN TEN PER CENT (10%) AND LESS THAN FORTY PER CENT (40%) BY WEIGHT OF THE TOTAL QUANTITY OF ZINC CHLORIDE AND MAGNESIUM SALT COMBINED. 